To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price of similar coins in the past is 307.88 euros.
- The coin has been auctioned 12 times, of which it has sold 8 times, indicating good demand.
- In previous auctions, hammer prices have varied, but there are examples of hammer prices exceeding 1000 euros for coins in better condition.

3. Starting Price and Estimates:
- The current starting price is 15 euros, which is relatively low compared to the average hammer price of similar coins.
- The average starting price of 111.45 euros and the average hammer price of 307.88 euros suggest there is significant potential for price increase.

4. Comparison with Previous Prices:
- In previous auctions, hammer prices have reached up to 1100 euros for coins in better condition (condition rating 100).
- For coins with similar condition (70), hammer prices have ranged from 30 to 100 euros in the most recent auctions.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 100 to 150 euros. This is based on the current condition, the hammer price history, and the demand observed in previous auctions.